In recent years, the communications industry has shown a growing interest in various types of wireless communications systems for communicating voice and/or data between numerous remote sites and a central location. It is well recognized that the use of a dedicated telephone facility for a conventional telephone system is not a convenient or economical option for all communications applications. For example, for many industrial applications, a central data collection site has a need for acquiring information from a variety of remotely located monitoring devices that collect data about the operation or performance of equipment. To overcome the limitations of the conventional telephone system, a two-way wireless communications link is often necessary to permit a response to a communication initiated from another location. In an attempt to solve the problem of supplying a response to an initial communication, the industry has offered various wireless communications systems, including two-way radios, cellular mobile radiotelephones, and paging systems.
A conventional radio communications system uses a base station transceiver located at a site for favorable radio propagation and a set of transceivers typically located in vehicles, such as for police or trucking dispatching systems, or at remote equipment sites that communicate data in response to a command signal from the base station transceiver. Most radio communications systems are useful for conducting communications between short distances, such as within the boundaries of a town or city, via a very high frequency (VHF) radio link.
Although conventional radio communications systems are useful for specialized communications applications, two-way radios are not widely accepted for general purpose communications. The use of two-way radios is generally regulated by the Federal Communications Commission (FCC) and the allocated frequency spectrum is relatively limited. Furthermore, the quality of communications is subject to the propagation conditions between communications sites. Two-way radio equipment is generally large and heavy and, as a result, is unlikely to be carried by a user at all times or to be installed in small or existing equipment.
Another form of two-way communications is a cellular mobile radiotelephone (CMR) system, which is connected to the extensive public switched telephone network (PSTN) and permits communications between a mobile radiotelephone user and anyone with a conventional telephone (or another radiotelephone). Typical CMR systems are characterized by dividing a radio coverage area into smaller coverage areas or "cell" using low power transmitters and coverage-restricted receivers. The limited coverage area enables the radio channels used in one cell to be reused in another cell. As a cellular mobile radiotelephone within one cell moves across the boundary of the cell and into an adjacent cell, control circuitry associated with the cells detects that the signal strength of the radiotelephone in the just-entered cell is stronger, and communications with the radiotelephone are "handed-off" to the just-entered cell. Thus, a CMR system can supply two-way communications for an array of cells, thereby supplying communications for a much wider area than conventional two-way radios.
Conventional radiotelephones generally offer both voice and data communications capabilities and, accordingly, the radiotelephone service is generally supplied at a cost that is commensurate with combined voice and data services. Nevertheless, this combination of both voice and data communications may exceed a user's requirement for communicating by only voice or data. In addition, real-time voice or data communications is not always desirable by a user who wishes only to receive a message without having a current activity disturbed. Similar to two-way radios, the frequency spectrum for the CMR system radio channels, particularly voice channels, is a limited resource.
Radiopaging systems include pagers, which are miniature receivers, and at least one radiopaging terminal having a transmitter that covers a selected geographic area containing numerous pagers. To respond to a page received via the conventional one-way radiopaging system, the paged party typically must find an available conventional telephone and initiate a telephone call to the party that initiated the page. Alternatively, the paged party can place a responsive call by use of a mobile radiotelephone, if available. Radiopaging systems having two-way communications capability for receiving a page and transmitting an acknowledge receipt of a page are also known. Such paging acknowledgment systems are most useful for local area "on-site" communications systems in view of the power limitations of the transmitters associated with the pagers.
Present radiopaging acknowledgment systems require a large capital investment for the purchase and installation of equipment to implement a two-way communications system that covers a wide communications area because the number of acknowledgment receivers (and transmitters) is a function of the limited transmitting power of the transmitter associated with each of the pagers. Although the radiopaging industry is interested in supplying a page acknowledgment to subscribers of paging services, the cost of implementing the paging acknowledgment system has discouraged many service providers from installing such paging acknowledgment systems.
To overcome the limitations of prior communications systems, the assignee for the present invention has developed a system for communicating data via a cellular network control channel of a CMR system. U.S. Pat. Nos. 5,526,401 and 5,546,444, which are assigned to the assignee for the present application and contain subject matter fully incorporated herein by reference, describe an adapted use of the existing architecture of a CMR system in an efficient and cost-effective manner to support communications via the CMR system, including collection and reporting of data obtained at remote sites. A data message system includes data reporting devices, at least one mobile switching center (MSC), and a data collection system connected directly or indirectly to the MSC or a Signal Transfer Point (STP). Each data reporting device can monitor the operation of a remote data source to collect selected data. The data reporting device can transmit a data message containing the selected data via a cellular network control channel of the CMR system when the data reporting device first identifies itself or "registers" for operation with the MSC. Alternatively, the data reporting device can send the selected data via the cellular network control channel in a data message formatted to represent a "call origination" signal. In turn, the MSC can send the data message to the data collection system via a communications link. In this manner, the data message system takes advantage of an installed base of cellular communications equipment by using the cellular network control channel for data communications between a central location and one or more remote sites.
The data reporting device of the data message system typically communicates with the MSC via the reverse overhead control channel (RECC) of the cellular network control channel. In contrast, the MSC can communicate with a cellular-compatible device, such as a data reporting device, via the forward overhead control channel (FOCC) of the cellular network control channel. The conventional technique for sending a message to a cellular mobile radiotelephone from an MSC is the transmission of a page message over the FOCC. For example, a conventional cellular mobile radiotelephone can be stimulated by a transmission of the MSC to locate the mobile telephone unit when an incoming call from a landline has been placed to this unit. The data requirement for this type of trigger message is minimal for conventional cellular communications and, consequently, each message is independently processed as a complete data packet. This works well for the paging operations conducted by an MSC with conventional cellular mobile radiotelephones via the FOCC, but significantly limits the amount of information that can be provided by the MSC to a data reporting device of the data message system developed by the assignee of this application.
In view of the foregoing, there is a need for transmitting a data sequence that extends beyond the capacity of a single conventional paging message of a CMR system. There also exists a need for adapting the paging mechanism of a CMR system to support the transfer of commands and data that exceed the scope of transmission via a single discrete paging message. The present invention overcomes the limitations of the prior paging system of a CMR system by sending a sequence of paging messages that can be aggregated at the reception site to obtain an increased data capacity for communications from an MSC to a cellular-compatible device.